This application is related to and claims priority, under 35 U.S.C. xc2xa7119, from Japanese Patent Application Nos. 2000-158235 and No. 2001-117737, filed in the Japanese Patent Office on May 29, 2000 and Apr. 17, 2001, respectively, and the entire contents of both Japanese patent applications are hereby incorporated by reference herein.
1. Field of the Invention
The present invention relates to a sheet feeding method and a sheet feeding device for image forming apparatuses, such as copying machines, printers, facsimile apparatuses, and printing apparatuses, and also relates to an image forming apparatus using the sheet feeding device.
2. Discussion of the Background
In image forming apparatuses, such as copying machines, printers, facsimile apparatuses, and printing apparatuses, sheets to be printed on are stacked in a sheet feeding part of the apparatuses and are separated one by one by a sheet feeding device of the apparatuses so as to be fed to an image forming part of the apparatuses. Known sheet feeding devices include feed and reverse rollers (FRR) type device, a friction roller (FR) type device, and a friction pad (FP) type device.
Recently, with the increase in the use of color images, a coated sheet having a superior smoothness has been widely used for sheets to be printed on in image forming apparatuses for obtaining a better image quality. The coated sheets tend to closely contact each other, either because of the smoothness of their surfaces or under the influence of humidity, in a sheet feeding part of image forming apparatuses, and thereby incomplete separation of the sheets occurs, resulting in double feeding of the sheets.
The following proposals are known with respect to improvement of sheet separation performance of sheet feeding devices of image forming apparatuses:
a) Japanese Patent Laid-Open Publication No. 5-201571 relates to a sheet feeding device which includes a feed roller rotating at a constant position and a separation member contacting the feed roller and in which sheets are fed into a nip between the feed roller and the separation member. For increasing the sheet separation performance, a vibrating member is arranged so as to contact the separation member at the backside thereof, and the separation member is vibrated by the vibrating member back and forth in a sheet feeding direction.
b) Japanese Patent Laid-Open Publication No. 5-213468 discloses that a mechanism for generating a force to stop conveyance of a sheet (i.e., the mechanism serving as a separation member) is elastically brought into contact with a rotating member (i.e., serving as a feed roller) rotating at a constant position. The separation member is vibrated by piezo-electric ceramics, so that the force to stop conveyance of a sheet by the separation member is freely suppressed and thereby, the sheet separation performance, corresponding to a change in the quality of sheets to be printed on, is obtained.
c) Japanese Patent Laid-Open Publication No. 5-330683 relates to a sheet feeding device in which a friction pad contacts a feed roller rotating at a constant position. For improving the separation performance, the friction pad is vibrated by a piezo-electric element so that the pressure of the friction pad is suppressed and the vibration is transmitted to the sheets to be printed on.
d) Japanese Patent Laid-Open Publication No. 6-100179 proposes to provide vibration, for increasing the sheet separation performance, to stacked sheets in a sheet feeding tray so that the stacked sheets are loosened.
In the above-described proposals a), b) and c), the separation member, which does not directly contact the sheet to be separated from the other sheets so as to be fed, is vibrated, and therefore the vibration is indirectly applied to the sheet to be separated in a thickness direction of the stacked sheets. Thereby, the sheet to be separated is not sufficiently vibrated, resulting in incomplete separation of the sheet. Also, in the above-described proposal d), the vibration is applied to the feeding tray, so that the sheet to be separated from the others to be fed is not directly vibrated, thereby resulting in incomplete separation of the sheet. Further, the vibration of the separation member by a high frequency wave does not provide the effect of the vibration over the entire part of a sheet. Therefore, the effect of loosening the stacked sheets is not sufficient to prevent non-feeding of the sheets.
The present invention has been made in view of the above-discussed and other problems and addresses the above-discussed and other problems.
Preferred embodiments of the present invention provide a novel sheet feeding method and a novel sheet feeding device that reliably prevents double feeding of sheets.
According to a preferred embodiment of the present invention, a method of feeding sheets includes the steps of: conveying the sheets between a feed roller and a separation member, the separation roller being pressed against and into contact with the feed roller, with a pressure applied between the feed roller and the separation member; and separating and conveying the sheets conveyed between the feed roller and the separation member one by one, wherein a cyclic change is provided in the pressure between the feed roller and the separation member.
In the above method, the cyclic change in the pressure may be provided from a side of the feed roller.
Further, the cyclic change in the pressure may be provided at a low frequency.
Furthermore, the feed roller may be cyclically pressed for providing the cyclic change in the pressure.
According to another preferred embodiment of the present invention, a sheet feeding device includes a feed roller and a separation member, wherein the separation member is pressed against and into contact with the feed roller with a pressure applied between the feed roller and separation member, and the sheets conveyed between the feed roller and the separation member are separated and conveyed one by one. The sheet feeding device further includes a pressing device configured to cyclically provide a change in the pressure between the feed roller and the separation member.
In the above sheet feeding device, the pressing device may be arranged at a side of the sheets, where the sheets are separated and conveyed one by one. Further, the pressing device may be provided to the feed roller. Furthermore, the pressing device may include a cam. Still furthermore, the above sheet feeding device may include a driving system driving the feed roller, and the pressing device may include a driving motor independent of the driving system of the feed roller. In this case, the motor may be selectively driven. Further, a rotation speed of the motor may be variable.
Further, in the above sheet feeding device, the pressing device may use a magnetic force.
Furthermore, the above sheet feeding device may include a driving system driving the feed roller, and the pressing device may be driven by a driving force from the feed roller driving system.
Still furthermore, in the above sheet feeding device, the sheet separation member may be one of: 1) a friction pad which is elastically pressed against and into contact with the feed roller; 2) a friction roller which is upwardly and elastically supported by an axis, the axis being rotated by a driving gear and a gear engaged with the driving gear and supported at one side thereof, and the friction roller being arranged at a free end side of the axis via a torque limiter, so as to be rotated only in a sheet feeding direction; and 3) a reverse roller which is upwardly and elastically supported by an axis, the axis being rotated by a driving gear and a gear engaged with the driving gear and supported at one side thereof, the reverse roller being arranged at a free end side of the axis via a torque limiter, so as to be rotated in a sheet feeding direction and a direction opposite the sheet feeding direction.
According to another preferred embodiment of the present invention, a sheet feeding device includes a feed roller and a reverse roller, wherein the reverse roller is pressed against and into contact with the feed roller with a pressure applied between the feed roller and the reverse roller. The reverse roller is upwardly and elastically supported by an axis which is supported at one side thereof and that is rotated by a driving gear and a gear engaged with the driving gear. The reverse roller is supported at a free end side of the axis and is arranged via a torque limiter, so as to be rotated in a sheet feeding direction and a direction opposite the sheet feeding direction. The sheet feeding device further includes a pressing device configured to provide a cyclic change in the pressure between the feed roller and the reverse roller, and the pressing device is arranged at a side of the reverse roller. The pressing device may use a magnetic force, and the pressing device may provide the pressure change more than one time as the reverse roller makes one rotation.
According to another preferred embodiment of the present invention, a sheet feeding device includes a feed roller and a friction roller, wherein the friction roller is pressed against and into contact with the feed roller with a pressure applied between the feed roller and the friction roller. The friction roller is upwardly and elastically supported by an axis which is supported at one side thereof and which is rotated by a driving gear and a gear engaged with the driving gear. The friction roller is arranged at a free end side of the axis via a torque limiter, so as to be rotated only in a sheet feeding direction. The sheet feeding device further includes a pressing device configured to provide a cyclic change in the pressure between the feed roller and the friction roller, and the pressing device is arranged at a side of the friction roller. The pressing device may use a magnetic force, and the pressing device may provide the pressure change more than one time as the friction roller makes one rotation.
Each of the above sheet feeding devices may further include a sheet guiding member to regulate advancement of the sheets downstream of the feed roller in the sheet feeding direction.
Further, in each of the above sheet feeding devices, the feed roller, the separation member, and the pressing device, may be integrally constructed in an unit which is attachable to and detachable from an image forming apparatus.
According to another preferred embodiment of the present invention, an image forming apparatus includes an image forming device, and a sheet feeding device configured to convey a sheet to the image forming device. The image forming device forms an image on the sheet conveyed from the sheet feeding device. The sheet feeding device includes a feed roller and a separation member, wherein the separation member is pressed against and into contact with the feed roller with a pressure applied between the feed roller and separation member. A plurality of the sheets, conveyed between the feed roller and the separation member, are separated and conveyed one by one by the sheet feeding device to the image forming device. The sheet feeding device further includes a pressing device configured to cyclically provide a change in the pressure between the feed roller and the separation member.
According to another preferred embodiment of the present invention, an image forming apparatus includes an image forming device, and a sheet feeding device configured to convey a sheet to the image forming device. The image forming device forms an image on the sheet conveyed from the sheet feeding device. The sheet feeding device includes a feed roller and a reverse roller pressed against and into contact with the feed roller with a pressure applied between the feed roller and the reverse roller. The reverse roller is upwardly and elastically supported by an axis which is supported at one side thereof and which is rotated by a driving gear and a gear engaged with the driving gear. The reverse roller is supported at a free end side of the axis and arranged via a torque limiter, so as to be rotated in a sheet feeding direction and a direction opposite the sheet feeding direction. A plurality of the sheets, conveyed between the feed roller and the reverse roller, are separated and are conveyed one by one to the image forming device. The sheet feeding device further includes a pressing device configured to provide a cyclic change in the pressure applied between the feed roller and the reverse roller, and the pressing device is arranged at a side of the reverse roller.
According to still another preferred embodiment of the present invention, an image forming apparatus includes an image forming device, and a sheet feeding device configured to convey a sheet to the image forming device, and the image forming device forms an image on the sheet conveyed from the sheet feeding device. The sheet feeding device includes a feed roller and a friction roller, wherein the friction roller is pressed against and into contact with the feed roller with a pressure applied between the feed roller and the friction roller. The friction roller is upwardly and elastically supported by an axis which is supported at one side thereof and which is rotated by a driving gear and a gear engaged with the driving gear. The friction roller is arranged at a free end side of the axis via a torque limiter, so as to be rotated only in a sheet feeding direction. A plurality of the sheets conveyed, between the feed roller and the friction roller, are separated and are conveyed one by one to the image forming device. The sheet feeding device further includes a pressing device configured to provide a cyclic change in the pressure between the feed roller and the friction roller, and the pressing device is arranged at a side of the friction roller.
According to another preferred embodiment of the present invention, a method of forming an image on a sheet includes the steps of: conveying a plurality of the sheets between a feed roller and a separation member, wherein the separation member is pressed against and into contact with the feed roller with a pressure applied between the feed roller and the separation member; separating and conveying the sheets conveyed between the feed roller and the separation member one by one to an image forming device, wherein a cyclic change is provided in the pressure applied between the feed roller and the separation member; and forming the image on the conveyed sheet with the image forming device.
In the above method, the cyclic change in the pressure may be provided from a side of the feed roller. Further, the cyclic change in the pressure may be provided at a low frequency. Furthermore, the feed roller may be cyclically pressed for providing the cyclic change in the pressure.